center is ground [horizontal], but ground won't cause the indicator problem unless something is causing hi and lo to be on at the same time ... standard wire colors are black for ground, green for high beam, tan for low, and there should be 2 green wires from the dimmer switch, one to the lights, one to the indicator, so the indicator is only powered when the high beams are powered, sounds like you may have that [green] wire to the indicator hooked to the terminal that brings power from the light switch [blue]
Bill
